TWI446956B - Method of improving performance of ultrafiltration or microfiltration membrane processes in backwash water treatment - Google Patents

Description

Method for improving the performance of ultrafiltration or microfiltration membrane procedures in backwash water treatment

The present invention relates to a method of treating backwash water by using a membrane system comprising a microfiltration membrane or an ultrafiltration membrane.

The backwash water is a medium filter or UF/MF membrane that is used to filter the raw water through a medium such as a medium filter, an ultrafiltration (UF) membrane, or a microfiltration (MF) membrane to filter the solids. Waste water stream produced after surface removal. Compared to raw water, such backwash water is a relatively concentrated stream of water containing high levels of contaminants such as suspended solids, colloidal materials, bacteria, viruses and other soluble organic matter. The net water recovery after media filtration or the first stage UF or MF system is about 85-90%, which means that 10-15% of the feed water is converted to concentrated or backwash water. This water is further treated in a second stage UF or MF system to increase the water recovery to 96-98%. The permeate water recovered from the second stage UF/MF is as clean as the first stage UF/MF and can be used in the program system or just as drinking water. However, since the backwash water obtained in the first stage UF/MF contains a relatively high amount of impurities, the second stage UF/MF system membrane will quickly foul and must have a lower flow rate than the first stage UF/MF system membrane. Under the operation. This phenomenon not only leads to a higher capital expenditure (more membranes), but also increases operating costs (frequent membrane cleaning). Therefore, it is currently of interest to minimize membrane fouling of the second stage UF/MF system so that the membrane can be operated over a longer period of time between cleaning steps, depending on the membrane selected Operate at a certain rate of flow, operate at a flow rate higher than currently available, or operate under the above conditions. In addition, it is of interest to reduce the number and/or size of the membranes so that capital expenditures for new systems containing the second stage UF/MF membrane for backwash water recovery are reduced.

The present invention provides a method of treating backwash water by using a membrane separation process, the method comprising the steps of: collecting backwash water in a container suitable for containing the backwash water; and using one or more water soluble polymers Treating the backwash water, wherein the water soluble polymer is selected from the group consisting of an amphoteric polymer, a cationic polymer, wherein the charge density is from about 5 mole percent to about 100 mole percent, the zwitterionic polymer, and a combination of the components; optionally mixing the water soluble polymer with the backwash water; passing the treated backwash water through a membrane wherein the membrane is an ultrafiltration membrane or a microfiltration membrane; and optionally The film is backwashed to remove solids from the surface of the film.

Definition of terms:

"UF" means ultrafiltration.

"MF" means microfiltration.

"Amphoteric polymer" means a polymer derived from both cationic monomers and anionic monomers, and possibly from other nonionic monomers. Amphoteric polymers can have a net positive or negative charge. Amphoteric polymers can also be derived from zwitterionic monomers and cationic or anionic monomers, and possibly, nonionic singles. Body obtained. Amphoteric polymers are water soluble.

"Cationic polymer" means a polymer having a positive total charge. The cationic polymer of the present invention is obtained by polymerizing one or more cationic monomers, by copolymerizing one or more nonionic monomers and one or more cationic monomers, by chloromethyl epoxide The alkane is condensed with a diamine or a polyamine or condensed with dichloroethane and ammonia or formaldehyde and an amine salt. The cationic polymer is water soluble.

"Zwitterionic polymer" means a polymer composed of a zwitterionic monomer and, possibly, other nonionic monomers. In zwitterionic polymers, all polymer chains and segments located in the polymer chain are precisely electrically neutral. Thus, the zwitterionic polymer represents a subgroup of an amphoteric polymer which, since both the negative and positive charges are introduced into the same zwitterionic monomer, will inevitably maintain electrical neutrality throughout the polymer chain and segments. The zwitterionic polymer is water soluble.

Preferred specific examples:

As described above, the present invention provides a method of treating backwash water by using a microfiltration membrane or an ultrafiltration membrane.

After collecting the backwash water and treating it with one or more water soluble polymers, the backwash water is passed through a membrane. In one embodiment, the film can be immersed in a tank. In another embodiment, the membrane is located outside of a feed tank containing the backwash water.

In another embodiment, the backwash water passing through the microfiltration membrane or ultrafiltration membrane can be passed further through one or more membranes. In a still further embodiment, the additional membrane can be a reverse osmosis membrane or a nanofiltration membrane.

Those skilled in the art will be familiar with a variety of backwash water treatment systems. In one embodiment, the leaching solution of the collected waste landfill may be passed through one or more filters or purifiers prior to passing through the ultrafiltration membrane or microfiltration membrane. In a further embodiment, the filter is selected from the group consisting of a sand filter, a multi-media filter, a cloth filter, a filter cartridge, and a bag filter.

The membrane used to treat the backwash water can have a variety of different physical and chemical properties.

Regarding physical properties, in one embodiment, the ultrafiltration membrane has a pore diameter ranging from 0.003 to 0.1 μm. In another embodiment, the microfiltration membrane has a pore size ranging from 0.1 to 0.4 [mu]m. In another embodiment, the membrane has a hollow fiber structure that can be a filtration mode from the outside or from the inside to the outside. In another embodiment, the film has a flat structure. In another embodiment, the film has a tubular structure. In another embodiment, the film has a porous structure.

Regarding chemical properties, in one embodiment, the film is a polymer. In another embodiment, the film is inorganic. In yet another embodiment, the film is stainless steel.

There are other physical or chemical film properties that can be used to carry out the claimed invention.

Various forms and amounts of chemistry can be used to treat the backwash water. In one embodiment, the backwash water collected by the media filter or the first stage UF/MF program can be treated with one or more water soluble polymers. The backwash water is optionally mixed with the added polymer by a mixing device. Many different types of mixing devices are known to those skilled in the art.

In another embodiment, these water soluble polymers typically have a molecular weight of from about 2,000 to about 10,000,000 otaves.

In another embodiment, the water soluble polymer is selected from the group consisting of an amphoteric polymer; a cationic polymer; and a zwitterionic polymer.

In another embodiment, the amphoteric polymer is selected from the group consisting of dimethylaminoethyl chloroformate quaternary ammonium sulfonate (DMAEA.MCQ)/acrylic acid copolymer, diallyldimethylammonium chloride/acrylic acid copolymer , dimethylaminoethyl chloroformate/N,N-dimethyl-N-methylpropenylaminopropyl-N-(3-sulfopropyl)ammonium betaine copolymer, acrylic acid/N , N-dimethyl-N-methyl acrylamidopropyl-N-(3-sulfopropyl) ammonium salt betaine copolymer, and DMAEA.MCQ/acrylic acid/N,N-dimethyl-N - a group consisting of methacrylamidopropyl-N-(3-sulfopropyl)ammonium betaine terpolymer.

In another embodiment, the water soluble polymer has a molecular weight of from about 2,000 to about 10,000,000 otaves. In yet another embodiment, the water soluble polymer has a molecular weight of from about 100,000 to about 2,000,000 otaves.

In another embodiment, the amphoteric polymer is present in an amount from about 1 ppm to about 2000 ppm of active solids.

In another embodiment, the amphoteric polymer has a molecular weight of from about 5,000 to about 2,000,000 otaves.

In another embodiment, the amphoteric polymer has a ratio of positive to negative charge equivalents of from about 3.0:7.0 to about 9.8:0.2.

In another embodiment, the cationic polymer is selected from the group consisting of polydiallyldimethylammonium chloride (polyDADMAC); polyethyleneimine; Amine; a polyamine crosslinked with ammonia or ethylenediamine; a condensation polymer of dichloroethane and ammonia; a condensation polymer of triethanolamine and pine oil fatty acid; poly(dimethylaminoethyl methacrylate sulfate) And a group of poly(dimethylaminoethyl chloroformate chloromethane quaternary salt).

In another embodiment, the cationic polymer is acrylamide (AcAm) and one or more selected from the group consisting of diallyldimethylammonium chloride; dimethylaminoethyl chloroformate quaternary ammonium salt; methyl a copolymer of dimethylaminoethyl acrylate chloromethane quaternary salt; and a cationic monomer in the group consisting of dimethylaminoethyl chloro chlorotoluene quaternary salt (DMAEA.BCQ).

In another embodiment, the cationic polymer has a positive charge between 20 mole percent and 50 mole percent.

In another embodiment, the cationic polymer is present in an amount from about 0.1 ppm to about 1000 ppm active solids.

In another embodiment, the cationic polymer has a positive charge of at least about 5 mole percent.

In another embodiment, the cationic polymer has a positive charge of 100 mole percent.

In another embodiment, the cationic polymer has a molecular weight of from about 100,000 to about 10,000,000 otaves.

In another embodiment, the zwitterionic polymer is from about 1 to about 99 mole percent of N,N-dimethyl-N-methylpropenylaminopropyl-N-(3-sulfopropyl) An ammonium salt betaine and one or more nonionic monomers having a percentage of from about 99 to about 1 mole.

Figures 1 through 3 show three possible backwash water treatment systems.

Referring to Figure 1, the backwash water obtained from the media filter or the first stage UF/MF system is collected in the backwash water container (1). The backwash water then flows through a conduit in which one or more polymers are added by means of the in-line addition (3). The treated backwash water then flows into a membrane unit (6) immersed in a tank (11). The polymer (10) may also be added to the tank (11) containing the immersion film. The immersion membrane can be an ultrafiltration membrane or a microfiltration membrane. The subsequent permeate (8) is then passed through an additional membrane (9) which may be a reverse osmosis membrane or a nanofiltration membrane, as appropriate.

Referring to Figure 2, the backwash water is collected in the backwash water container (1). The backwash water then flows through a conduit in which one or more polymers are added by means of the in-line addition (3). The treated backwash water is subsequently passed into a mixing tank (2) where it is mixed by a mixing device (7), and additional polymer (4) is optionally added to the mixing tank (2). The treated backwash water is then passed through a pre-filter (5) or a purifier (5). The treated backwash water then flows through a conduit into a membrane unit (6) that is immersed in a tank (11). The polymer (10) is optionally added to the tank (11) containing the immersion film. The immersion membrane can be an ultrafiltration membrane or a microfiltration membrane. The subsequent permeate (8) is then passed through an additional membrane (9) which may be a reverse osmosis membrane or a nanofiltration membrane, as appropriate.

Referring to Figure 3, the backwash water is collected in the backwash water receiving container (1). The backwash water then flows through a conduit in which one or more polymers are added by means of the in-line addition (3). The treated backwash water is subsequently passed into a mixing tank (2) where it is mixed by a mixing device (7), and additional polymer (4) is optionally added to the mixing tank (2). Processed back Wash the water and then pass through a pre-filter (5) or a purifier (5). The treated backwash water then flows through a conduit into a membrane unit (6) which does not contain a microfiltration membrane, ie, contains an ultrafiltration membrane. The subsequent permeate (8) is then passed through an additional membrane (9) which may be a reverse osmosis membrane or a nanofiltration membrane, as appropriate. The resulting permeate is collected for various purposes as is known to those skilled in the art.

In another embodiment, the membrane separation procedure is selected from the group consisting of a cross-flow membrane separation procedure; a semi-terminal flow membrane separation procedure; and a terminal flow membrane separation procedure.

The following examples are not intended to limit the scope of the claimed invention.

Example

Membrane efficiency was investigated by measuring turbidity and conducting actual membrane filtration studies on polymer treated backwash water samples. Turbidity was measured on a Hach turbidity meter (Hach, Ames, IA) with a sensitivity of 0.06 NTU (scattering turbidity units), while membrane filtration studies were performed in a terminal filtration mixing chamber (Millipore, Bedford, MA), where the membrane The area was 42 cm ² , the agitation rate was 50 rpm, the transmembrane pressure (TMP) was 10 psig, and the UF membrane was 100,000 amps.

Example 1

In individual cans, incremental organic (cationic and anionic) polymers, inorganic products, and combinations of inorganic and organic products are slowly added to the backwash water sample (obtained from the US Southern Water Filtration Plant) and The magnet mixer was mixed for about 3 minutes. After the treated solid was allowed to settle in the tank for 10 minutes, the turbidity of the supernatant was measured.

It can be seen from Table 1 that the turbidity of the cationic organic polymer is remarkably lowered, but the cationic inorganic product or the blend of the inorganic product and the organic polymer is not lowered.

Example 2

Using the procedure illustrated in Example 1, the backwash water treated with product A (core shell DMAEA.MCQ/AcAm) was directly filtered through a UF membrane and monitored with a volume concentration factor ("VCF") (ie, The ratio of the volume of the material to the volume of the retentate) changes the permeate flow rate. The results are shown in Figure 4. Figure 4 also shows the filtration results of the treated backwash water which was pre-settling.

It can be seen from Fig. 1 that the permeate flow rate is about 100% higher than that of the control group at a given volume concentration factor, and the permeate flow rate of the treated solid is more than 200% higher than that of the control group.

Example 3

Using the procedure described in Example 1, was carried out using a UF membrane The wash back water was treated with two different doses of product B (DMAEA.MCQ/BCQ/AcAm) prior to filtration. The results are shown in Figure 5.

As can be seen from Figure 5, increasing the dose of product B increases the permeate flow rate, wherein after treatment with 625 ppm of product B, the permeate flow rate is about 100% higher than the control group, for example, its VCF is 1.3.

1‧‧‧ receiving container

2‧‧‧ mixing tank

3‧‧‧Adding in the pipeline

4‧‧‧ polymer

5‧‧‧Pre-filter or purifier

6‧‧‧ membrane unit

7‧‧‧Mixed device

8‧‧‧Subsequent permeate

9‧‧‧ film

10‧‧‧ polymer

11‧‧‧ slot

Figure 1 illustrates a general procedure system for treating backwash water comprising a microfiltration membrane/ultrafiltration membrane wherein the membrane is immersed in a tank and an additional membrane for further processing from the microfiltration Membrane/ultrafiltration membrane permeate.

2 illustrates a general procedure system for treating backwash water, comprising a mixing tank, a purifier/prefilter, and a microfiltration membrane/ultrafiltration membrane, wherein the membrane system is immersed in a tank, and An additional membrane is used to further treat the permeate from the microfiltration membrane/ultrafiltration membrane.

Figure 3 illustrates a general procedure system for treating backwash water comprising a mixing tank, a purifier/prefilter and a microfiltration membrane/ultrafiltration membrane, wherein the membrane is located in a backwash containing water The outside of the feed tank, and an additional membrane for further processing of the permeate from the microfiltration membrane/ultrafiltration membrane.

Figure 4 shows the increase in flow rate with product A.

Figure 5 shows the increase in flow rate with product B.

1‧‧‧ receiving container

3‧‧‧Adding in the pipeline

6‧‧‧ membrane unit

8‧‧‧Subsequent permeate

9‧‧‧ film

10‧‧‧ polymer

11‧‧‧ slot

Claims (20)

A method for treating backwash water by using a membrane separation procedure comprising the steps of: a. collecting backwash water in a container suitable for containing the backwash water; b. polymerizing with one or more water soluble Treating the backwash water, wherein the water soluble polymer is selected from the group consisting of amphoteric polymers; cationic polymers, wherein the charge density is from about 5 mole percent to about 100 mole percent; zwitterionic polymers; and combinations thereof In the group formed; c. mixing the water-soluble polymer with the backwash water as appropriate; d. passing the treated backwash water through a membrane, wherein the membrane is an ultrafiltration membrane or a microfiltration membrane; And e. backwashing the film as appropriate to remove solids from the surface of the film. The method of claim 1, wherein the driving force for passing the backwash water through the film is positive or negative. The method of claim 1, wherein the ultrafiltration membrane has a pore size ranging from 0.003 to 0.1 μm. The method of claim 1, wherein the microfiltration membrane has a pore size ranging from 0.1 to 0.4 μm. The method of claim 1, wherein the membrane is immersed in a tank. The method of claim 1, wherein the film is located outside a feed tank containing the backwash water. The method of claim 1, wherein the water soluble polymer has a molecular weight of from about 2,000 to about 10,000,000 otaves. The method of claim 1, wherein the amphoteric polymer is selected from the group consisting of dimethylaminoethyl chloroformate chloromethane quaternary salt/acrylic acid copolymer, diallyldimethylammonium chloride/acrylic acid copolymer, Dimethylaminoethyl chloroformate/N,N-dimethyl-N-methylpropenylaminopropyl-N-(3-sulfopropyl)ammonium betaine copolymer, acrylic acid/N, N-Dimethyl-N-methacrylylamidopropyl-N-(3-sulfopropyl)ammonium betaine copolymer, and DMAEA.MCQ/acrylic acid/N,N-dimethyl-N- A group consisting of methacrylamidopropyl-N-(3-sulfopropyl)ammonium betaine terpolymer. The method of claim 1, wherein the amphoteric polymer is present in an amount from about 1 ppm to about 2000 ppm of active solids. The method of claim 1, wherein the amphoteric polymer has a molecular weight of from about 5,000 to about 2,000,000 otaves. The method of claim 1, wherein the amphoteric polymer has a ratio of cationic charge equivalent to anionic charge equivalent of from about 3.0:7.0 to about 9.8:0.2. The method of claim 1, wherein the cationic polymer is selected from the group consisting of polydiallyldimethylammonium chloride; polyethyleneimine; polyepiamine; and cross-linking with ammonia or ethylenediamine Epithetamine; condensation polymer of dichloroethane and ammonia; condensation polymer of triethanolamine and pine oil fatty acid; poly(dimethylaminoethyl methacrylate sulfate); and poly(dimethylaminoethyl acrylate) In the group consisting of chloromethane quaternary salts). The method of claim 1, wherein the cationic polymer is acrylamide and one or more selected from the group consisting of diallyldimethylammonium chloride; dimethylaminoethyl chloroformate quaternary ammonium salt; a copolymer of a dimethylaminoethyl acrylate chloromethane quaternary salt; and a cationic monomer in the group consisting of dimethylaminoethyl chloro chlorotoluene quaternary salt. The method of claim 1, wherein the cationic polymer is present in an amount from about 0.1 ppm to about 1000 ppm active solids. The method of claim 1, wherein the cationic polymer has a cationic charge of at least about 5 mole percent. The method of claim 1, wherein the cationic polymer has a cationic charge of 100 mole percent. The method of claim 1, wherein the cationic polymer has a molecular weight of from about 500,000 to about 10,000,000 otaves. The method of claim 1, wherein the zwitterionic polymer is from about 1 to about 99 mole percent of N,N-dimethyl-N-methylpropenylaminopropyl-N-(3) a sulfopropyl) ammonium salt betaine and one or more nonionic monomers having a percentage of from about 99 to about 1 mole. The method of claim 1, further comprising passing the polymer-treated backwash water through a filter or a purifier before the backwash water passes through the membrane. The method of claim 1, further comprising passing the filtrate from the membrane through an additional membrane.